So we are running as root and have all privileges in our process and are
passing all on to our children. We also own the file (and it is on a local ZFS filesystem not over NFS), and it is writable by us and our group, everyone in fact.
So lets try and modify it:

Before I started this I made the file immutable. That means that regardless
of what privileges(5) the process has and what POSIX permissions or NFSv4/ZFS ACL
it has we can't delete it change it nor can we even change the POSIX permissions
or the ACL. So how did we do that ? Without good old friend chmod:

# chmod S+ci /tank/fs/hamlet.txt

Or more verbosely:

# chmod chmod S+v immutable /tank/fs/hamlet.txt

See chmod(1) for more details. For those of you running OpenSolaris 2008.05 releases then you need to change the default PATH to have /usr/bin in front of /usr/gnu/bin or use the full path to /usr/bin/chmod. This is because these extensions are only part of the OpenSolaris chmod command not the GNU version. The same applies to my previous posting on the extended output from ls.

In response to UX-admin. No they didn't the extensions are completely compatible. This doesn't break or change any of the traditional UNIX permissions syntax for chmod(1) and you aren't forced to use any of the new stuff.

David: No on Coincidence at all it is intended to provide the matching functionality to BSD. There are other system flags that were added to support CIFS (SMB), such as Archive, System, Hidden, AntiVirus.

UX-admin: It doesn't let root override it because that is the whole point of it. It can be turned off by doing 'chmod S-v file' then root can do what it can normally do to the file. Note that immutable isn't the only flag we have there are others, some for CIFS and some others to match what BSD and Linux already had.